Processes for the treatment of cast-iron melts are known in which gas, for example air (as an oxygen carrier) or oxygen, is blown onto the surface of a cast-iron melt to effect a movement of the bath such that the metal is swept centrifugally above its normal quiescent surface. This treatment is used to promote the tendency of a given flowable cast-iron melt to solidify as gray cast iron. In this process, however, a strong development of smoke is observed above the melt so that the process can only be employed in foundries provided with gas-evacuating and filtering systems to prevent endangering the health of the operating personnel.
It is also known to provide a process for the refining of steel melts in which oxygen is blown onto the upper surface of a steel melt through a lance (see German open application DT-OS No. 14 33 486). Even in this case a continuing evolution of smoke occurs. The smoke evolution can be positively effected by the lance described in this application although not completely avoided.
In smelters for the preparation of steel melts, therefore, fume-collection and exhaust devices are required and the fume-treatmentsystems are expensive to construct and operate although they are necessary to prevent environmental pollution. However, even the special cleaning devices are not fully satisfactory.
Fume and smoke cleaning and evacuating apparatus of the latter type is not usually provided in cast iron smelters or foundries. If it is desired, therefore, to treat a melt such that smoke evolution may occur, without constructing such evacuating and cleaning apparatus, the process can only be carried out in special furnaces, i.e. the types of furnaces in which smelting can be effected are limited.
Furthermore, it has been found that a larger problem arises in the treatment of a cast-iron melt with a gas, namely, the proper control of the gas flow for an optimum treatment process. If melt temperature is used as the actual value input to a control system for supplying oxygen or another treatment gas to the melt, relatively complex control means must be provided and experiments must be undertaken to determine the relationship between temperature and gas feed. The same holds true with all conventional controlled apparatus for the regulation of gas flow in melt-treatment systems used heretofore.